1. Field of the Invention
The present invention relates to an image signal converting apparatus and method, and more particularly, to a method of and an apparatus for converting a frame rate using time shifting and motion compensation.
2. Description of the Related Art
Commonly, a frame, which is one image picture, is made up of minimum picture elements, each picture element called a pixel. Resolution is determined according to the number of pixels included in the frame. A frame having a maximum resolution of 1,920×1,080 is 1,920 pixels wide and 1,080 pixels long. A frame rate is the number of frames transmitted per second. When an image signal such as a TV signal is transmitted, an appropriate number of frames per second are transmitted on the basis of the eyesight characteristics of a human body.
A frame rate of a film image signal produced for showing a movie is commonly 24 frames per second (fps). However, a frame rate of an National Television System Committee (NTSC) standard image signal is 30 fps. Therefore, the frame rate of the film image signal must be expanded into 30 fps (60 fields per second) for applying to an NTSC standard format.
FIG. 1 illustrates a conventional frame rate converting method suitable for converting a 24 fps digital image signal into a 30 fps digital image signal.
Referring to, FIG. 1, each of 24 input frames F1, F2, F3, F4, . . . , F24 is divided into a top field f1 and a bottom field f2. New frames F1, F2, F3′, F4′, F5 . . . , F30 are generated using the top fields f1 and the bottom fields f2 of the 24 input frames F1, F2, F3, F4, . . . , F24. That is, the new frame F3′ is generated from the top field f1 of the frame F2 and the bottom field f2 of the frame F3, and the new frame F4′ is generated from the top field f1 of the frame F3 and the bottom field f2 of the frame F4.
Likewise, if new frames are generated from adjacent frames where autocorrelation is high, 24 frames are converted into 30 frames.
The conventional frame rate converting method used to convert a frame rate using cross type field repetition generates discontinuity in a picture (commonly, called a motion judder effect) due to simple field repetition. For example, if there is an object flying from the right to the left in a picture, the motion of the object is inconveniently displayed due to discontinuous portions.